SidecarFlip wrote:
Took my cover off on my old one and pop riveted in some aluminum hardware store screen.
This /\
Simple, easy, cheap. If your RV repair place says it can't be done, it simply means "they" don't want to do it because it's not an "off-the-shelf" product, but instead something that they have to actually think about and fabricate. Any type of fine mesh wire from Home Depot, Lowes, TSC, etc, can be attached to the inside (or easier, the outside) of the vent cap using rivets, screws, or even zip ties, going all the way around and extending down to the roof.
Heck you don't even need to remove the cap or attach the mesh. Simply cut a strip of the mesh about 3" high and just long enough to go all the way around the vent cap. Attach the two ends together, and then set it around the cap, like a fence, touching the vent cap all the way around. Simply remove it when you leave.